Some communication systems allow the user of a terminal, such as a personal computer, to conduct voice or video calls over a packet-based computer network such as the Internet. Such communication systems include voice or video over Internet protocol (VoIP) systems. These systems are beneficial to the user as they are often of significantly lower cost than conventional fixed line or mobile networks. This may particularly be the case for long-distance communication. To use a VoIP system, the user installs and executes client software on their terminal. The client software sets up the VoIP connections as well as providing other functions such as registration and authentication. In addition to voice communication, the client may also set up connections for other communication media such as instant messaging (“IM”), SMS messaging, file transfer and voicemail.
One type of communication system for packet-based communication uses a peer-to-peer (“P2P”) topology. To enable access to a peer-to-peer system, a user executes P2P client software supplied by a P2P software provider on their terminal, and registers with the P2P system. When the user registers with the P2P system, the client software is provided with a digital certificate from a server. This may be referred to as a “user identity certificate” (UIC). Once the client software has been provided with the certificate, then calls or other communication connections can subsequently be set up and routed between end-users (“peers”) of the P2P system without the further use of a server in the call set-up. Instead, the client looks up the required IP addresses from information distributed amongst the P2P client software on other end-users' terminals within the P2P system. That is, the address look-up list is distributed amongst the peers themselves. Once the IP address of a callee's terminal has thus been determined, the caller's P2P client software then exchanges UIC certificates with the callee's P2P client software. The exchange of these digital certificates between users provides proof of the users' identities and that they are suitably authorised and authenticated in the P2P system. Therefore the presentation of digital certificates provides trust in the identity of the users.
It is therefore a characteristic of peer-to-peer communication that, once registered, the users can set up their own communication routes through the P2P system in at least a partially decentralized manner based on distributed address look-up and/or the exchange of one or more digital certificates, without using a server for those purposes. Further details of an example P2P system are disclosed in WO 2005/008524 and WO 2005/009019.
VoIP or other packet-based communications can also be implemented using non-P2P systems that do use centralized call set-up and/or authorisation, e.g. via server.
A problem with packet-based communications is that their accessibility to users is limited. In particular, such communications are most commonly accessed using a client application installed on personal computer. This has a disadvantage in that its use may be limited, since personal computers are often not located in a place where the user is either familiar of comfortable with making phone calls. For example, a personal computer is often located in a study which for many users is not the most natural or comfortable environment for making personal calls. Whilst packet-based communication systems can also be accessed via certain mobile devices, these generally do not have sufficient processing resources, bandwidth or display screens to offer a full range of features, such as video calling.
It would therefore be desirable to make packet-based communications more accessible to users. One way to do this would be to run a packet-based communication client on a processor embedded in a familiar household media appliance like a television set or set-top box for plugging into a television. Embedded in this context means within the casing of the appliance. The ability to integrate an embedded processor into a television set or set-top box is known, and indeed many modern televisions and boxes already contain a processor for performing at least some of the digital signal processing required to decode and output viewable television signals to the screen.